You can turn off iCloud functions and remove the iCloud Drive app from your iPhone. However, since iCloud is built into your iPhone's operating system, it cannot be removed completely.
Steps
Part 1 of 2: Sign out of iCloud

Step 1. Open Settings
This is a gray app that represents a gear (⚙️) and is usually located on the Home screen.

Step 2. Tap your Apple ID
This is the section at the top of the screen where your name and profile picture are displayed if you have added one.
- If you are using an older version of iOS, select iCloud in place.

Step 3. Scroll down and choose Sign Out
This option is located at the bottom of the screen.
- If prompted, enter your Apple ID password and then press Switch off.
- Signing out of iCloud will disable features such as Clothing and Find my iPhone if you had them enabled.

Step 4. Select the data you want to keep
Drag the app sliders Calendar, Contacts, News, Reminders, Where Safari in position We (green) if you want to keep a copy of this data on your iPhone.

Step 5. Choose Sign Out
This option is in the upper right corner. All iCloud functions are now disabled on your iPhone.
Part 2 of 2: Remove the iCloud Drive app

Step 1. Find the iCloud Drive app
It's a white app that represents a blue cloud.

Step 2. Press and hold on the app
Keep pressing until all apps start to move.

Step 3. Select ⓧ
This symbol can be found in the upper left corner of the app.

Step 4. Choose Remove
You deleted the iCloud Drive app from your iPhone.